1. Field of the Invention
The present invention relates to a method of and an apparatus for correcting a read position error in subscanning direction in scanning and inputting of image data by a line image sensor arranged in parallel with the main scanning direction.
2. Description of the Prior Art
In recent years, requirement is increased for reading a large original in high resolution as demand is increased for organization of a data base by various technical materials such as design drawings and maps. In the field of electronic process for commercial printing, for example, it is also required to read an original in extremely high resolution. Efforts have been made to increase a pixel number of a line image sensor, whereas the current upper limit thereof is about 5000 pixels. For example, 24,000 pixels are required in order to read an original of A1 (Japan Industrial Stardard) size (about 600 mm in width) in resolution of 40 lines/mm and, therefore, the original must be divided to be read, into five in the main scanning direction by employing five line image sensors of 5,000 pixels. In this case, each line image sensor must read image signals on the same main scanning line, as a matter of course. Pixel size of a line image sensor tends to be reduced as the pixel number thereof is increased. In the case of 5,000 pixels, for example, each pixel is in extremely small size of 7 .mu.m.times.7 .mu.m. Therefore, it is extremely difficult to so strictly arrange a plurality of line image sensors that the respective line image sensors correctly read on an absolutely identical main scanning line. Even if complete arrangement is performed in manufacturing, it is almost impossible to so maintain mechanical accuracy that no deviation is caused by vibration in transportation, time transition, temperature change and the like.
Although the problem of misarrangement between plural line image sensors cannot arise in the case of employing only a single line image sensor, it is still difficult to maintain strict positional accuracy of the sensor for a long time like the aforementioned case of employing a plurality of line image sensors, and a slight inclination error may be caused with respect to the main scanning direction. Thus, read position error in the subscanning direction will be inevitably caused to lower the quality of read images to some extent in either case, and the problem of such lowering of picture quality is serious particularly in the aforementioned field requiring image reading of high resolution.